Image intensifiers and the like

ABSTRACT

Method of manufacturing a channel plate having membranes or films at an end of each channel, comprising allowing a liquid to extend by capillary action along the channels to form a meniscus at the channel mouths, solidifying the menisci to provide temporary supports, forming the membranes on the temporary supports and removing the temporary supports to leave the membranes behind. Also, the channel plate produced by this method.

United States Patent 1191 Stone Jan. 1, 1974 [54] IMAGE INTENSIFIERS ANDTHE LIKE 3,327,151 6/1967 Adams et a1 313/104 1 1 "m stone, surrey,2:532:12? 13/132? ififiiiiittii: .1132??? England FOREIGN PATENT ORAPPLICATION [73] Assignee: U.S. Philips Corporation, New S S York N'Y1,175,599 12/1969 Great Er taln 313/103 1,216,497 3/1969 GreatBritain... .313/104 [22] Filed: Nov. 8, 1971 788,057 6/1968 Canada313/103 [30] Foreign Application Priority Data Nov. 18, 1970 GreatBritain 54,817/70 [52] US. Cl. 29/592, 29/25.14 [51] Int. Cl. H0ls 4/00[58] Field of Search 29/592, 25.14; 313/103, 104

[56] References Cited UNITED STATES PATENTS 2,922,906 1/1960 Day 313/1033,243,642 3/1966 Gebel 313/103 3,319,318 5/1967 Taimuty 29/592 3,562,8942/1971 Rome 29/592 Primary Examiner-Richard J. Herbst AssistantExaminerM. J. Keenan Attorney-Frank R. Trifari 57] ABSTRACT Method ofmanufacturing a channel plate having membranes or films at an end ofeach channel, comprising allowing a liquid to extend by capillary actionalong the channels to form a meniscus at the channel mouths, solidifyingthe menisci to provide temporary supports, forming the membranes on thetemporary supports and removing the temporary supports to leave themembranes behind. Also, the 'channel plate produced by this method.

17) (1151;113:190 'rsiazv'in s IMAGE INTENSIFIERS AND THE LIKE Thisinvention relates to electron multiplier and image intensifier devices.More particularly the invention relates to channel intensifier devices(referred to also more briefly as channel plates) and to electronictubes employing such devices. Such devices are secondary-emissiveelectron-multiplier devices comprising a matrix in the form of a platehaving a large number of elongate channels passing through itsthickness, said plate having a first conductive layer on its input faceand a separate second conductive layer on its output face to actrespectively as input and output electrodes.

Secondary-emissive intensifier devices of this character are described,for example, in British Pat. specifications, No. 1,064,073 (PHB 31172),No. 1,064,074 (PHB 31173), No. 1,064,076 (PHB 31184), No. 1,090,406(co-pending British Applications 32722/63 and 36758/63: PHB 31211) andNo. l.l54,5l5 (copending British Application 22339/67; PHB 31754), whilemethods of manufacture are described in British Patent SpecificationsNo. 1,064,072 (PHB 31171 Comb.) and No. 1,064,075 (PHB 31183).

in the operation of all these inte'nsifier devices a potcntialdifference is applied between the two electrode layers of the matrix soas to set up an electric field to accelerate the electrons, which fieldestablishes a potential gradient created by current flowing throughresistive surfaces formed inside the channels or (if such channelsurfaces are absent) through the bulk material of the matrix.Secondary-emissive multiplication takes place in the channels and theoutput electrons may be acted upon by a further accelerating field whichmay be set up between the output electrode and a suitable target, forexample a luminescent display screen.

With channel plates the distribution and crosssections of the channelsand the resistivity of the matrix are such that the resolution andelectron multiplication characteristic of any one unit area of thedevice is sufficiently similar to that of any other unit area for thepurposes envisaged, the greatest uniformity being usually required forimaging.

lf such a channel plate is used in an imaging tube or system, the latterwill be referred to for convenience as an image intensifier? tube orsystem rather than as an image converter" tube or system even inapplications vwhere the primary purpose is a change in the wavelength ofthe radiation of the image.

In channel plate technology cases have arisen where it is desirable toprovide a very thin membrane to obturate the end of each channel. Thiscan be extremely difficult to achieve, particularly if the membraneshave to be sufficiently thin to be electron permeable or if it isdesired to avoid penetration of membrane material to the walls of themouths of the channels beyond a fraction of a diameter.

Other difficulties can arise as illustrated by reference to one ofthemethods used by Applicants to form channel plates for image intensifiersemploying a conductive film over the input face (and over the mouths ofthe channels) in accordance with British Patent Specification 1,175,599(PHB 31816). In this particular method an aluminium film is evaporatedonto a support film of nitrocellulosewhich is placed on the channelplate and then baked away. It is difficult to prepare large films whichare uniform and free of small holes. Use of this method also results incarbonaceous residues from the nitrocellulose remaining between thealuminium and the input electrode (usually of nichrome). Also, thealuminium film produced has poor adhesion on channel plates having largeopen areas.

It is an object of the present invention to provide an improved methodof channel plate manufacture which permits such problems to be overcome.

The invention provides a method of manufacturing a channel plateincluding in addition a membrane obturating an end of each channel or achannel plate wherein such membranes are formed as extensions of theinput electrode of the plate so that said electrode and membranes form,together, a continuous layer, which method includes the steps of:

A. allowing a liquid to extend by capillary attraction along thechannels so as to form a meniscus at the mouth of each channel B.rendering the meniscus surfaces solid so that they provide temporarysupports for the formation of the desired membranes C. forming saidmembranes on said temporary supports, and

D. removing the temporary supports so as to leave meniscus-shapedself-supporting membranes lf desired membranes are of the kind describedin the aforesaid British Pat. specification 1,175,599 (PHB 31816) andthe chosen membrane material is aluminium, then the above process isapplied to the input face of the channel plate and the aluminium isapplied, e.g., by vacuum deposition on the temporary supports. If thechannel plate is of the kind having an input electrode distinct from themembrane, such electrode is formed on the channel plate matrix (usuallynichrome on a glass matrix) before the aluminizing process. Conversely,if the plate is of the type wherein the membranes and input electrodeform, together, a single continuous layer, then the process according tothe present invention is applied to the channel plate matrix without theprevious provision of a separate input electrode.

As will be understood from the following description, the liquid may forexample be a simple liquid or it may be dispersion or emulsion. As forthe methods of solidifying the meniscus support surfaces, variouschemical and physical processes can be used and these include freezing(in the case ofa simple liquid) and breaking an emulsion. Moreover, someof said processes (e.g. heating) may involve removal of the liquid fromthe channels as well as solidification of the meniscus'support surfaces(as will be explained in the last of the examples, this situation mayrequire means for preventing premature loss of liquid from thechannels).

Specific embodiments of the invention will now be described by way ofexample as applied to the formation of aluminium membranes on a glassmatrix which may or may not have a separate nichrome input electrode.

Example (a): A freezing method This may be carried out by allowing asuitable liquid to extend into the channels by capillary action,freezing the liquid, evaporating the metal layer on the meniscussurfaces, allowing the frozen liquid to melt and finally removing theliquid. A method of evaporating metals on to a frozen liquid is knownand can be a very clean method. However, it is difficult to retain themeniscus at the mouth of the channels because the liquid contracts intothe channels on freezing. It is also difficult to remove the liquidwithout breaking the aluminium film.

Example (b): Formation of a meniscus film from a dispersion This methodprovides each channel with exactly the same quantity of support filmforming material, so that uniformity can be achieved regardless ofchannel plate diameter.

i. Practical requirements 1. a suitable dispersion of very fineparticles 2. a convenient method of causing the dispersed particles tocome out of the liquid (known as breaking the emulsion) and form a filmon the surface.

3. a film forming material with suitable properties such as strength andgood adhesion to nichrome and/or glass.

4. a film forming material which can be readily and completely removedafter serving its purpose as a temporary support film.

ii. Practical methods using Emulsion Lacquers Dispersions of very fineparticles (e.g. 0.111.) of or ganic polymers in water are available asemulsions and referred to as emulsion lacquers. The emulsion has verylow viscosity like water, so that it will readily fill the smallestchannels normally used.

The particles can be quickly caused to come out of the water (breakingthe emulsion) and form a film on the meniscus by a wide range ofphysical and chemical means. The physical means include the use of heat,ultrasonics and electrical means. The chemical methods include theaddition of electrolytes or surfactants and changing the pH value.

All of these methods cause the particles in the water to come togetherat the surface. A film of lacquer is then formed on the surface of thewater.

For the use of emulsions with channel plates the plate can be supportedabove the floor of a dish with the input side uppermost. The emulsionlacquer is poured into the dish until it reaches the bottom of theplate. The emulsion lacquer then rises by capillary attraction in thechannels and forms meniscus surfaces at the input side. The emulsion isthen broken by one of the methods referred to above. The lacquer layerformed on the meniscus surface also adheres at the edge of the meniscusto the nichrome or glass at the mouth of each channel. This layer ishardened (and also the water under the lacquer is removed) by warmingthe channel plate in an oven. The film oflacquer of meniscus shaperemains across the mouth of each channel. The aluminium is thenevaporated and the lacquer removed by baking. The aluminium filmproduced is, of course, of meniscus shape across each channel.

Emulsions of various film forming polymers can be used, butmethacrylates appear to be the most suitable at present. They can bereadily removed after use by baking as is known from their use astemporary support films in the aluminising of T.V. tubes.

Example (c): A Preferred Emulsion Method in Detail The emulsion used ispoly-2-ethoxyethyl methacrylate in water. The polymer content used inonly 0.3 percent by weight.

The emulsion is poured slowly into the dish containing the channel platewhich is supported off the floor of the dish. When the emulsion levelreaches the bottom of the channel plate it rises in the channels and canbe observed when it reaches the top of the channels. In order to breakthe emulsion the dish and channel plate are warmed to 50C and thistemperature maintained for ten minutes. The lacquer film will then haveformed on the meniscus surface. The channel plate is then transferred toan oven at C for 2 hours in order to harden the film and remove thewater under the lacquer film.

The channel plate is then placed in a vacuum evaporation equipment, thepressure reduced to 10 torr and the aluminium layer (e.g., 1,000A.thick) deposited on the channel input side. The channel plate is thenbaked in air in an oven at 350C for 30 minutes to remove the lacquer.

When emulsion methods using heat to remove the liquid (as in Examples(b) and (c)) are applied to channel plates having channel diameterssmaller than p. there is an increasing risk that the heating processwill cause premature loss of liquid from the channels. As the column ofliquid in a channel is shortened by removal ofliquid from the open end(i.e., the end remote from the meniscus film) capillary attractionincreases at both ends and, if this occurs before the meniscus surfacehas solidified sufficiently, the meniscus film can be punctured or tornby the capillary forces.

This can be prevented by retaining additional liquid outside, but incontact with, the remote ends of the channels. This can for example beachieved by using a method wherein, during solidification of themeniscus surfaces, additional liquid is retained outside, but in contactwith, the remote ends of the channels (i.e. the ends remote from saidmeniscus surfaces) thereby to prevent premature loss of liquid from thechannels. An example of the use of a mesh for this purpose will be givenunder a separate heading since it is applicable not only to the abovespecific Examples. However, before describing the use of a mesh, afurther detailed Example will be described which is similar to Example(c).

Example (d): A second Preferred Emulsion Method in Detail 1. Preparationof the Emulsion Lacquer The emulsion used is Poly-2-ethoxyethylmethacrylate in water. lt has a solids content of 33 percent which isdiluted to 0.6 percent solids before use.

It is essential to purify the emulsion lacquers before use in channelsbecause the impurities have a detrimental effect on channel performance.These impurities consist of inorganic salts, emulsifying agents andunreacted monomer which are required for the preparation of theemulsion. Purification is carried out by ultra filtration.

2. Preferred Method of Breaking the Emulsion This is carried out bydirecting radiant heat directly on the emulsion menisci at the ends ofthe channels. An infra-red lamp is used and located so that the top ofthe lamp bulb is 10 cmsbelow the channel face. The heating time dependson the size of the channel plate but 2-5 minutes are normally required.

3. Procedure for Forming the Supports Sufficien-t purified lacquer ispoured into a roundbottom dish to give a liquid surface greater than thechannel plate diameter. The channel plate is placed in the lacquer sothat only its lower surface is immersed. The lacquer rises in thechannels by capillary attraction and forms a meniscus at the top of eachchannel.

The channel plate is gently removed from the lacquer and the surplusdrops of lacquer hanging from the lower surface and removed by wipingwith a filter paper previously wet with water.

The channel plate is then inverted and supported horizontally by a clampon the sides of the channel plate so that both faces are accessible.

A mesh having a diameter slightly smaller than that of the plate is thencompletely immersed in a dish of lacquer and then withdrawn when a layerof emulsion will be found over all the holes in the mesh. The mesh isplaced on top of the channel plate. Additional lacquer is then run intothe gap between the channel plate and the mesh until the gap is filled.

The lower face of the channel plate is now heated in order to cause theemulsion particles to form a solid plastic film on the liquid meniscussurfaces on the lower ends of the channels. The heat is applied by aninfra-red lamp from a distance cms below the channel plate for severalminutes.

After the lamp is switched off the channel plate is allowed to standuntil all the emulsion between the mesh and plate has disappeared.Emulsion then remains only in the channels above the solidified film atthe bottom of the channels.

The mesh is removed from the channel plate which is then transferred toan oven at 70C for 1 hour to dry out the liquid in the channels. Theplate is put in the oven with the solidified film on the bottom side.

The channel plate is then placed in a vacuum evaporation equipment.

4. Deposition of Metal The channel plate is located on a rotating table(the centre of which is heated) cms above the aluminium source. Thetable surface is at an angle of 45 to the horizontal. The evaporatingchamber is then pumped down below 10" Torr, and the table rotated atabout rpm while a 500 A. layer of aluminium is deposited on the lacquerlayer. The channel plate is then baked in air in an oven at 350C forminutes to remove the lacquer leaving an aluminium film in each channelin the shape of a meniscus.

A non-reflecting black layer is required for some types of devices. Thisblack layer can be provided on top of the first aluminium layer byevaporating aluminium through an inert gas such as nitrogen or argon ata pressu re above l0 Torr.

The Use of a Mesh for Fine Channel Plates A special problem is found inusing emulsion lacquers in fine channel plates (channel diameters of l00p. or less) which does not arise in capillary tubes of larger diameter(e.g., 500 microns). When the latter are filled with lacquer while beingheld vertically and heated from below the reduction in liquid volume byevaporation results in the top meniscus falling while the bottommeniscus stays in position. This allows a film to be formed withoutdifficulty at the mouth of the tube.

However-in channel plates with channel diameters of I00 microns or less,upon heating from below, the liquid menisci withdrawn from both ends.Furthermore, the initial rate of withdrawal from the channel mouth isvery rapid so that any film formation is not at the mouth of thechannel.

This problem can be met by retaining the meniscus at the mouth of thechannel which is being heated to secure film formation.

' cover the top surface with water since it will immediately fallthrough the channels. it is necessary to prevent this happening byproviding some support for the reservoir of liquid but not too muchsupport or it will not flow into the channels and keep the channels fullof lacquer.

These requirements are met by the provision of a mesh located about0.5-1 mm above the top surface of the channel plate and parallel to it.The channels are filled with water and the space between the channelplate and mesh is filled with water, the latter space acting as thereservoir. The capillary forces associated with the mesh aresufficiently strong to restrain the water while still allowing thisexcess liquid to act as a reservoir.

The result of this method is to maintain the meniscus at the mouth ofthe channel during the period of heating so that a satisfactory solidfilm can be produced.

The mesh has a further advantage in the'subsequent removal of thereservoir water since it can rapidly evaporate through the mesh.

The mesh can be of woven wire or electroformed, made of nickel orstainless steel, and with a pitch about 0.8 mm. The mesh is at least 2mm smaller in diameter than the channel plate it is used on. It can besupported 0.5 mm above the channel plate by bending down the edges ofthe mesh by that amount.

Care is necessary in the preparation of emulsions of high purity andalso in ensuring that no residues of the lacquer remain in the channels.

Advantages ofthese preferred versions (c) and (d) of the process are:

a. A high degree of uniformity of the membranes.

b. No carbonaceous layer between nichrome and aluminium.

c. Large dust particles do not stick to the lacquer, since it is all inthe channel mouths and thus below the face of the channel plate (thiscontrasts with the earlier method described herein with reference toPat. specification No. 1,175,599: PHB 31816). Therefore, particles whichwould otherwise block several channels can be blown off and do not causethe formation of pinholes. Any dust particle small enough to reach thelacquer will only occupy one channel and will be an acceptable blemish.

d. improved adhesion of the aluminium on channels of high open area,i.e., on a thin-walled matrix.

e. As a minor advantage, no inflammable solvents are involved.

Channel plates in accordance with the invention can be used in imagingtubes, for example an image intensifier tube of the proximity type or atube of the electron-optical diode or inverter type.

The invention may also be used for other imaging tubes, for examplecathode-ray display tubes and camera tubes.

What we claim is:

l. A method of manufacturing a channel plate including in addition amembrane obturating an end of each channel or a channel plate whereinsuch membranes are formed as extensions of the input electrode of theplate so that said electrode and membranes form, together, a continuouslayer, which method includes the steps of:

A. allowing a liquid to extend by capillary attraction along thechannels so as to form a meniscus at the mouth of each channel B.rendering the meniscus surfaces solid so that they provide temporarysupports for the formation of the desired membranes C. forming saidmembranes on said temporary supports, and

D. removing the temporary supports so as to leave meniscus-shapedself-supporting membranes.

2. A method as claimed in claim 1 employed for the provision of metallicmembranes, wherein metal is evaporated onto the temporary supports.

3. A method as claimed in claim 2 wherein the metal is aluminium.

4. A method as recited in claim 1 wherein the liquid in the channels isfrozen so as to solidify the meniscus support surfaces.

5. A method as recited in claim 1 wherein the liquid in the channels isan emulsion and said emulsion is bro- Lil LII

ken so that the dispersed particles in each channel are separated fromthe liquid and travel to one end of the liquid column to form a meniscussupport surface.

6. A method as claimed in claim 5 wherein the action of heat is used tosolidify the meniscus surfaces and to remove the liquid.

7. A method as recited in claim 5 wherein during s0- lidification of themeniscus surfaces, additional liquid is retained outside, but in contactwith, the remote ends of the channels, said channel ends being remotefrom said meniscus surfaces, thereby to prevent premature loss of liquidfrom the channels.

8. A method as recited in claim 7 wherein a mesh is held close to theface of the channel plate remote from the desired supports, said meshhaving such pitch and such spacing from the channel plate as to enableit to retain liquid between itself and the plate.

9. A method as recited in claim 5 wherein the emulsion is a dispersionof organic polymer particles in water.

10. A method as recited in claim 3, further comprising the step ofproviding on said aluminum membrane a non-reflecting black layer, saidlayer being produced by evaporating aluminum through an inert gas.

223 UNITED STATES-PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,781,979 r Dated January 1, 1974 Inventor-(s!) HENRY DERMOTT STONE Itis certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

C olumn 1, line 16, cHete (PHIB 31172)" g '1 line 17, delete (PI-1B31173) and (PHB 31184) lines 18 and 19, delete (co-pending.. PHB3l2ll)"line '19 delete (co-' line 20, delete the entire line 1 lines 22 and 23,delete" K 31171 Comb.) 7

line-23, delete 31183)";

line 62, delete (PHB 318E567".

Column 2 lines 2, 33, & 55, change "nichrome" to -Nichrome-;

lines 26 & 27, delete MBHB 31816)"; 3

line 42 after "be" insert --a.

Column 3, lines 17 & 47, change "nichrome" to --Nichrome--;

line- 39, change "floor" to -bottom--;

line 61, change "in Detail" to -Suitab1e for Channel Diameters Greaterthan 100 Microns--;

323 UNITED STATES PATENT OFFICE Page 2 CERTIFICATE OF CORRECTION PatentNo. 3, 781, 979 Dated January 1, 1974 Inventory?) HENRY DERMOTT STONE Itis certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 4 insert --Examp1e .(d) A Preferred Emulsion 1 line 15, MethodSuitable for Channel Diameters of 100 Microns or Less-.

Column 4, line 39, change to and insert --the other steps beingdescribed below Sections 1 Column 5, line 8', change "A" to --To retainadditional 7 liquid (as mentioned above) aline 34, delete line 35,change "heatedl" to --located.

Column 6, lines 39-41, delete in their entirety-;

line 45, change "nichrome" to -Nichrome--;

line 51, delete "PHB 31816)".

Signed and sealed this 23rd da of April 19714..

(SEAL) Attest:

EDWARD MJ LETCHERJB. C. MARSHALL DAM 'Attesting Officer 1 Commissionerof Patents

1. A method of manufacturing a channel plate including in addition amembrane obturating an end of each channel or a channel plate whereinsuch membranes are formed as extensions of the input electrode of theplate so that said electrode and membranes form, together, a continuouslayer, which method includes the steps of: A. allowing a liquid toextend by capillary attraction along the channels so as to form ameniscus at the mouth of each channel B. rendering the meniscus surfacessolid so that they provide temporary supports for the formation of thedesired membranes C. forming said membranes on said temporary supports,and D. removing the temporary supports so as to leave meniscusshapedself-supporting membranes.
 2. A method as claimed in claim 1 employedfor the provision of metallic membranes, wherein metal is evaporatedonto the temporary supports.
 3. A method as claimed in claim 2 whereinthe metal is aluminium.
 4. A method as recited in claim 1 wherein theliquid in the channels is frozen so as to solidify the meniscus supportsurfaces.
 5. A method as recited in claim 1 wherein the liquid in thechannels is an emulsion and said emulsion is broken so that thedispersed particles in each channel are separated from the liquid andtravel to one end of the liquid column to form a meniscus supportsurface.
 6. A method as claimed in claim 5 wherein the action of heat isused to solidify the meniscus surfaces and to remove the liquid.
 7. Amethod as recited in claim 5 wherein during solidification of themeniscus surfaces, additional liquid is retained outside, but in contactwith, the remote ends of the channels, said channel ends being remotefrom said meniscus surfaces, thereby to prevent premature loss of liquidfrom the channels.
 8. A method as recited in claim 7 wherein a mesh isheld close to the face of the channel plate remote from the desiredsupports, said mesh having such pitch and such spacing from the channelplate as to enable it to retain liquid between itself and the plate. 9.A method as recited in claim 5 wherein the emulsion is a dispersion oforganic polymer particles in water.
 10. A method as recited in claim 3,further comprising the step of providing on said aluminum membrane anon-reflecting black layer, said layer being produced by evaporatingalumInum through an inert gas.